By way of background on the general subject of a duplex automatic document handler (DADF) with a stacking input tray at least partially overlying a stacking output tray, and the platen, for a light-lens copier, there is noted the Xerox Corporation "5034" copier document handler, and illustrative Xerox Corp. patents thereon such as U.S. Pat. Nos. 5,000,438 or 5,001,124. However, it may be seen that this is an N to 1, bottom feeder system, and the document path is longer and more complex, including feeding the documents across the full platen width to the end of the output tray which is opposite from the input end of the input tray. Another DADF is disclosed in U.S. Pat. No. 4,941,023, and other art is noted therein on DADF's and coordination with trayless duplex copy sheet loops.
It is known that a constant velocity transport (CVT) (moving document) scanner can provide rapid (more closely spaced) document exchange times at the imaging station, to help, e.g., provide scanning at greater than 50 scanned documents per minute.
There is patent art on CVT duplex (both sides imaged) document handlers specifically for electronic (digital) imaging with a raster input scanner (RIS). A RIS may be either of the full width array (FWA) type, or a smaller RIS CCD array or chip with lens image reduction. Such patents on duplex document handlers specifically for Electronic Front End scanners (EFEs) (and/or digital copiers), include U.S. Pat. No. 4,536,077 issued Aug. 20, 1985 to James C. Stoffel. Also, an XDJ published May/June 1983 by Richard E. Smith, Vol. 8, No. 3 p 263. Both references disclose two separate imaging stations for the two sides of the duplex document, and the latter shows two RIS's. Also noted are U.S. Pat. No. 4,571,636 by Itoh and U.S. Pat. No. 4,429,333, both references disclose using the same CCD array carriage (RIS) for both the duplex CVT image station as for platen scanning, in the same plane, although the two imaging areas are separated.
Also disclosed in the CVT patents are twin-nip CVTs moving the document past a stationary RIS between CVT nips on opposite sides of the RIS, which provides good document motion quality. Also, with angled nips the document can be accurately deformed between the two nips towards the RIS to provide sheet beam strength and positive sheet engagement against the RIS platen or slit.
By way of further background art on various other document feeders specifically for electronic (digital) imaging, noted are U.S. Pat. Nos. 5,026,044; 4,506,301; 4,536,077; 4,380,389; 4,451,030; 4,496,984; and 4,607,951. Also, U.S. Pat. No. 4,295,167 (FIG. 5 especially) or related U.S. Pat. Nos. 4,287,536; 4,496,984; 4,471,386; and 4,447,830 (the latter three show simple straight-through document feeding rather than a folded or inverting document path). Also, U.S. Pat. No. 4,743,974 filed in 1987; and U.S. Pat. No. 4,967,233.
1 to N document sequencing is preferred for scanner (EFE) document input for several reasons. First, it desirably facilitates employing a top feeder and face-up input loading. This enables higher sheet capacities, better sheet separation and feeding reliability, and less smear generation provided by top sheet feeding from a document stack loaded face up; as compared to a bottom of stack sheet separator/feeder. Secondly, 1 to N document input eliminates a non-copying document counting circulation or "precount cycle" for simplex to duplex copying (to make duplex copies from either odd or even numbers of simplex originals). Thirdly, 1 to N input enables correct automatic page numbering concurrently with page image input. Fourthly, it is compatible with existing printer architectures and existing FAX standards, and thus enables one common document handler to be used for both digital copying and FAX. Fifthly, with 1 to N document input, there is no incoming data stream delay before job printing can be started and tested. That is especially important if documents with detailed graphics, or other high pixel count files, are being transmitted by telephone lines or other relatively low bandwidth (and thus low baud rate) communication systems. 1 to N sequencing is also compatible with most electronic filing software.
A simple, relatively inexpensive, and accurate approach to document handling simplex/duplex originals and maintaining 1 to N sequencing in such printing systems has been a goal in the design, manufacture and use of electrophotographic printers. This need has been particularly recognized in scanning of a mix set of originals (i.e. simplex and duplex originals) so that the originals can be fed, scanned, inverted (if necessary), and then delivered face down in the proper sequence into the same output tray. The need to provide accurate and inexpensive document handling has become more acute, as the demand for high quality, relatively inexpensive scanners has increased.
The present invention overcomes various of the above-discussed problems of duplex automatic document handlers, and provides various of the above features and advantages.